1. Field of the Invention
The present invention relates to an image capture apparatus including a neutral density (ND) filter which is inserted into or withdrawn from an optical path of an image capture optical system.
2. Description of Related Art
An image capture apparatus with an ND filter which is inserted into or withdrawn from an optical path of an image capture optical system in accordance with the brightness of an object is disclosed in Japanese Patent Application Laid-Open No. 2003-283923.
FIG. 3 is a block diagram showing an example of a conventional image pickup apparatus 300 of this kind. The image pickup apparatus may be an electronic still camera or a video camera. In the figure, a reference numeral 301 denotes a lens which is the image capture optical system. A reference numeral 302 denotes the ND filter (achromatic color light reduction filter), which reduces the transmitting light amount of the image capture optical system. A reference numeral 303 denotes an iris for adjusting the light amount. A reference numeral 304 denotes an image capture device such as a CCD. A reference numeral 305 denotes a correlated double sampling (CDS)/auto gain control (AGC) circuit. A reference numeral 306 denotes a luminance signal detection circuit for detecting a luminance signal from an image signal output from the CDS/AGC circuit 305. A reference numeral 311 denotes an iris control signal generation circuit which generates a control signal for controlling the iris 303 according to the luminance information output from the luminance signal detection circuit 306. A reference numeral 308 denotes an iris driver which drives the iris 303 based on a control signal from the iris control signal generation circuit 311.
A reference numeral 310 denotes an ND filter insertion/withdrawal switch-over switch for switching over the insertion or the withdrawal of the ND filter 302 in conformity with the intension of a user. The switch 310 is not the switch such as a slide switch, which holds the state thereof and results in the storage of the on/off state thereof. The switch 310 is generally the switch such as a push switch, which does not hold the state thereof and results in the non-storage of the on/off state thereof. In other words, the switch 310 is the switch for switching over the ND filter 302, which is in either sate of the insertion state thereof and the withdrawal state thereof, from one state to the other state by each same operation. The user cannot judge which state of the insertion state and the withdrawal sate the ND filter 302 is in only by viewing the state of the switch 310.
A reference numeral 312 denotes an ND control signal generation circuit which generates a control signal for controlling the switch-over of the ND filter 302 from one sate to the other state according to a key operation of the ND filter insertion/withdrawal switch-over switch 310. A reference numeral 309 denotes an ND driver for driving the ND filter 302 based on a control signal from the ND control signal generation circuit 312. A reference numeral 307 denotes an electric power switch operated when the user switches over a power source of the main body of the camera to the on-state thereof or the off-state thereof.
When the user carries out the key operation of the electric power switch 307, the power source of the main body of the camera is turned on, and the image capture apparatus 300 having the configuration mentioned above starts image capturing. As the luminance signal used when exposure is controlled, a luminance signal including high frequency components of an image signal output from the CDS/AGC circuit 305 is used. The luminance signal is detected by the luminance signal detection circuit 306, and then is sent to the iris control signal generation circuit 311. The iris control signal generation circuit 311 compares the luminance signal detected by the luminance signal detection circuit 306 with a reference value (the level of appropriate exposure) previously determined to keep the luminance signal constant, and generates an iris control signal. More specifically, the iris control signal generation circuit 311 compares the luminance signal detected by the luminance signal detection circuit 306 with the reference value, and generates a control signal for operating the iris 303 to move it toward closing in case of “the luminance signal>the reference value.” On the other hand, the iris control signal generation circuit 311 generates a control signal to operate the iris 303 toward opening in case of “the luminance signal<the reference value.” The control signals generated in such a way are supplied to the iris driver 308, and the iris 303 is driven. By always carrying out the control mentioned above, it becomes possible to make the exposure state be in the optimum state.
Here, the ND filter 302 is described in detail. The ND filter 302 is configured so as to be in the withdrawal state thereof just after the user has turned on the power source of the main body of the camera by operating the electric power switch 307. When the user wishes to insert the ND filter 302 into the optical path from this state, the ND filer 302 is inserted therein by the key operation of the ND filer insertion/withdrawal switch-over switch 310 by the user. Moreover, when the ND filter 302 which is in the insertion state thereof is desired to be withdrawn from the optical path, the ND filer 302 is withdrawn from the optical path by another key operation of the ND filter insertion/withdrawal switch-over switch 310. For example, in the case where brightness of an object is high out of doors or the like, a diffraction phenomenon is sometimes brought about owing to a decrease of the diameter of the iris 303, and results in a deterioration of the image quality of the image of the object. Inserting the ND filter 302 into the optical path in order to avoid this disadvantage will make it possible to obtain a good quality image. Moreover, in the case where brightness of an object is low within doors or the like, withdrawing the ND filter 302 from the optical path in order to obtain good sensitivity will make it possible to obtain a good quality image.
Using the block diagram of FIG. 3, the operation of the ND filter 302 at the time of the insertion into or the withdrawal from the optical path is described. When a key operation of the ND filer insertion/withdrawal switch-over switch 310 is once carried out by a user in the case where the ND filter 302 is in the withdrawal state thereof from the optical path, the ND control signal generation circuit 312 generates a control signal for inserting the ND filter 302 into the optical path. The generated control signal is supplied to the ND driver 309, and then the ND filter 302 is inserted into the optical path. When another key operation of the ND filer insertion/withdrawal switch-over switch 310 is carried out by the user in this state, the ND control signal generation circuit 312 generates a control signal for withdrawing the ND filter 302. The control signal is supplied to the ND driver 309, and the ND filter 302 is withdrawn from the optical path.
Next, by reference to the flowchart of FIG. 4, control operations of the iris 303 and the ND filter 302 immediately after the turning-on of the power source of the main body of the camera are described.
At a step 401, a user carries out a key operation of the electric power switch 307, and the power source of the main body of the camera becomes in the on state thereof. Then, the ND filter insertion/withdrawal switch-over switch 310 is made to be in an invalidated state at the next step 402. And, at the next step 403, the luminance signal detection circuit 306 detects a luminance signal including high frequency components of an image signal output from the CDS/AGC circuit 305. At the successive step 404, the iris control signal generation circuit 311 compares the detected signal with a predetermined reference value (an appropriate exposure level) to generate a control signal for controlling the iris 303. For example, when the detected signal is larger than the reference value as a result of the comparison of the detected signal with the reference value, the iris control signal generation circuit 311 generates a control signal for controlling the iris 303 toward the closing thereof. On the other hand, when the detected signal is smaller than the reference value, the iris control signal generation circuit 311 generates a control signal for controlling the iris 303 toward the opening thereof. Then, at the next step 405, the iris control signal generation circuit 311 supplies the control signal generated at the step 404 to the iris driver 308 to drive the iris 303.
At the next step 406, the iris control signal generation circuit 311 generates a control signal for withdrawing the ND filter 302 from the optical path in order to create a previously withdrawn state of the ND filter 302 after the turning-on of the power source. Then, at the next step 407, the iris control signal generation circuit 311 supplies the control signal generated at the step 406 to the ND driver 309 to withdraw the ND filter 302 to the outside of the optical path. Then, at the next step 408, the iris control signal generation circuit 311 validates the ND filter insertion/withdrawal switch-over switch 310, which has been invalidated at the step 402.
The camera having the ND filter mentioned above has been scarcely adopted as a camera in a popular type class. The following reasons can be considered of the nonadoption of the camera having the ND filter: the using method of the camera becomes troublesome; the main body of the camera becomes larger; the cost of the camera becomes expensive; and the like. However, the camera having the ND filer has been considerably generally adopted as a camera in a quality type class.
Now, in the image capture apparatus 300 mentioned above, it cannot be judged only by viewing the state of the switch 310 which state of the insertion and the withdrawal the ND filter 302 is in. Consequently, when a user does not remember which state of the insertion and the withdrawal the ND filter 302 is in at the time of turning off the power source of the main body of the camera, it is difficult for the user to immediately grasp which state of the insertion and the withdrawal the ND filter 302 is in when the power source is next turned on. Moreover, when the ND filter 302 is in the insertion state thereof, the amount of the light reaching the image capture device 304, of course, decreases more than the decreased amount at the time of being in the withdrawal state thereof. Consequently, it is impossible to obtain sufficient luminance at the time of carrying out photographing within doors. Accordingly, the image capture apparatus mentioned above, as shown in FIG. 4, controls the ND filter 302 to be in the withdrawal state thereof just after the turning-on of the power source of the main body of the camera. However, under such a configuration, even when recording is desired to be begun immediately after the turning-on of the power source of the main body of the camera, the ND filter 302 is always in the withdrawal state thereof. Consequently, for example, when the brightness of an object is low within doors or the like, good photographing can be carried out. But, when the brightness of an object is high out of doors or the like, because the ND filter 302 is being left in the withdrawal state thereof, the iris 303 becomes the state of having a small diameter, and the diffraction phenomenon is brought about.
It is, of course, possible to start recording in this state as it is, but, because the diffraction phenomenon has the possibility of causing the deterioration of image quality, good photographing cannot be always carried out. In such a case, the user is required to carry out the key operation of the ND filter insertion/withdrawal switch-over switch 310 in order to switch over the insertion/withdrawal state of the ND filter 302, and to switch over the ND filter 302 from the withdrawal state thereof to the insertion state thereof. That is, in the case where the photographing when the user wants to start recording immediately after the turning-on (activation) of the power source of the main body of the camera is to be performed in the state in which the brightness of the object is high out of doors or the like, the user is required to carry out the operation of inserting the ND filter 302 into the optical path. Because the user has to insert the ND filter into the optical path by carrying out the key operation of the ND filter insertion/withdrawal switch-over switch 310, the image capture apparatus 300 has a problem of the impossibility of the instantaneous starting of recording.